This invention relates to optical circulators, in particular to an optical circulator with adjustable alignment.
Non-reciprocal devices are used in microwave and optical communications for selectively directing signals from one port to another. With the growth in fiber optic communications, there is an increasing demand for non-reciprocal components that are suitable for use with fiber optic systems. For example, isolators are used for increasing the stability of the frequency and power produced by single mode semiconductor lasers by reducing the power of light feeding back into the laser. As fiber optic systems become more sophisticated, for example with the advent of wavelength division multiplexing (WDM), add/drop demultiplexing and bidirectional transmission, there is an increased need for advanced components such as optical circulators.
Many optical circulators are of the three port design, in which light incident at the first port is transmitted through the circulator to the second port. This light may then be transmitted to another optical device. Light entering the circulator from the second port is transmitted through the circulator to a third port. The third port may be situated close to the first port and, in some cases, the first and third ports include optical fibers held together by a common holder, such as a ferrule.
Present approaches to circulator design often rely on the accuracy of the position of the fibers at the ports of the circulator and/or the precision of the alignment of the optical components of the circulator. Typically, conventional circulators are aligned by moving the first port and/or second port relative to each other. However, if the third port is held in a particular position relative to the first port, which is often the case, there is either no freedom or only very limited freedom to adjust the position of the third port to optimize the coupling of light from the second port, into the third port. Consequently, there may be a power loss if the ports and components of the circulator are not accurately positioned.
Generally, the present invention relates to optical circulators with one or more alignable reflecting components that permit the optimization of light coupling into the ports of the circulator. In particular, an optical circulator includes a reflective polarizer adapted to transmit light having a first polarization direction and reflect light having a second polarization direction orthogonal to the first polarization direction. A first non-reciprocal polarization rotator is positioned to transmit light propagating in a first direction from the reflective polarizer, and a second non-reciprocal polarization rotator is positioned to transmit light reflected by the reflective polarizer after propagating in a second direction opposite to the first direction. A first reflector reflects light from the second non-reciprocal polarization rotator to the reflective polarizer and a third non-reciprocal polarization rotator is positioned to transmit light reflected by the first mirror. A second reflector reflects light from the third non-reciprocal polarization rotator to the reflective polarizer. At least one of the first mirror and second mirror is adjustable to alter a propagation path of a light beam propagating through the optical circulator.
In another embodiment of the invention, a circulator includes means for propagating light from a first port to a second port through a reflective polarizer; means for propagating light from the second port to a third port through the reflective polarizer; means for rotating polarization of light passing from the first port to the second port and from the second port to the third port; and means for rotating light polarization and for reflecting light deflected by the reflective polarizer back to the reflective polarizer, the means for reflecting light being adjustable so as to alter a propagation path of light propagating between one of the first and second ports and the second and third ports.
A method of circulating light from a first port to a third port includes propagating light from a first port through a reflective polarizer to a second port, propagating the light from the second port into the reflective polarizer, and reflecting the light from the reflective polarizer to a first mirror. The method further includes reflecting the light from the first mirror through the reflective polarizer to a second mirror, wherein at least one of the first and second mirrors is adjustable to alter a propagation path of the light propagating between the first and second mirrors, reflecting the light from the second mirror into the reflective polarizer; and reflecting the light from the reflective polarizer to a third port.
The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The Figures and the detailed description which follow more particularly exemplify these embodiments.